OSLO  Warmer, wetter weather brought on by global warming could increase outbreaks of the plague, which has killed millions down the ages and wiped out one third of Europe's population in the 14th century, academics said.

Migratory birds spreading avian flu from Asia today could also carry the plague bacteria westward from their source in Central Asia, Nils Stenseth, head of a three-day conference on the plague and how it spreads, told Reuters on Monday.

"Wetter, warmer weather conditions mean there are likely to be more of the bacteria around than normal and the chance of it spreading to humans is higher," he said.

The European Union-funded group has just finished analysing Soviet-era data from Kazakhstan which show a link between warmer weather and outbreaks of the plague.

This analysis was important as it had not previously been clear whether warmer conditions encouraged the bacteria, fleas and rats to grow or killed them off, Stenseth said. Plague bacteria are often carried by fleas on rats.

ADVERTISEMENT

"But if it becomes too hot it would kill off the fleas and rodents," he said.

Many scientists say a build-up of heat-trapping gases from burning fossil fuels is pushing up temperatures around the world and changing Earth's climate.

KILLER BACTERIA

The plague -- caused by the virulent, aggressive and mutating Yersinia Pestis bacteria -- periodically breaks out in Kazakhstan and other Central Asian countries and has been carried around the globe by fleas on the back of rats, birds and in clothing for centuries, Stenseth said.

"If you treat it with antibiotics in a few days it should be all right, but if you leave it any longer there is a 60 percent chance of death."

In the 14th century the plague killed around 34 million people and some academics believe it reappeared every generation, including the Great Plague of London in 1665-66.

"The link is very important and it is also important to link it back to the Black Death in the 1300s because there were the kind of weather conditions then -- warmer and wetter -- that we predict for the future," Stenseth said.

"After 1855, when it (plague) reappeared again, there were once again similar weather conditions."

Scientists are still unsure why the plague originates in Central Asia. It has spread throughout the world, including recently to east Africa, and this is due at least partly to birds.

"Many, many bird species are spreading bacteria from one place to another, from one rodent to another, by carrying fleas," Stenseth said.

"That birds spread the bacteria is not in question but how important that is in the big picture is not yet clear."

Unlike the bird flu virus, which infects and kills domestic birds, plague-carrying fleas do not harm the birds that carry them.